Abstract: To study the radiation damage caused by radioactive plume in leeward direction after dirty bomb (radiological dispersal device) terrorism attacks, the simulation model of atmospheric dispersion was set up based on the random walk method. With specific source term and dose simulation models, the radiation doses of leeward regions caused by a ¹³⁷Cs dirty bomb were simulated in atmospheric stability classes of A-F in low wind conditions. The results show that the leeward radiation doses are influenced significantly by atmospheric stability. The more unstable the atmosphere is, the further the transverse diffusion of radioactive plume is, meanwhile, the faster the dose decreases with the leeward distance and the smaller the polluted areas for dose exceeding public limit. When the atmospheric stability class is F, the area of contaminated regions where the dose exceeds public dose limit and the radiation dose in 1 km leeward direction are 4 times and 10 times higher than those of class A respectively.